In the production of packaging containers of a single-use disposable type for various types of drinks, e.g. juice and milk, use is often made of a laminated packaging material which is cut, folded and sealed for the formation of a liquid-tight, filled and sealed packaging container. A common material type consists of a laminate which comprises a central, relatively thick carrier layer of fibrous material, e.g. paper, which is coated on either side with layers of thermoplastic material. Possibly, other layers may also be included, for example barrier layers such as aluminium foil or some form of barrier plastic such as, for instance, EVOH. In order to facilitate the forming of the packaging container, the packaging laminate is weakened in a linear pattern of crease lines which, by compressing above all the carrier layer of the laminate, facilitate its folding. Normally, the crease lines extend both parallel to the longitudinal direction of the web and at different angles thereto, for example transversely or obliquely over the material web.
In the production of packaging laminates of the above-outlined type, a relatively wide web of the fibrous material subsequently forming the carrier layer of the laminate is provided with external, liquid-tight thermoplastic layers of, for example, polyethylene with the aid of a laminator unit. The plastic layers are extruded in linear configuration over the entire width of the web, and cooled compression rollers are employed to ensure that the plastic melts into and is permanently bonded to the fibrous layer. Possible additional layers of, for example, aluminium foil are thereafter applied, whereupon an external layer of liquid-tight thermoplastic completes the laminate production process. Immediately hereafter, the laminate is, in prior art production methods, provided with the desired pattern of crease lines, which is realised with the aid of two cooperating, counter-rotating rollers between which the laminate passes. The rollers, which are provided with male and female tools, respectively, compress the packaging laminate so that the desired pattern of crease lines is obtained. The thus produced and crease-lined, relatively wide web of starting material is then divided by means of cutting tools into the desired number of parallel tributary or part webs, each one of which being of a width which corresponds to the width of the material consumed for producing one packaging container of the relevant type. The part webs are then rolled up into reel form in order to be able to be stored in a compact manner until such time as the material is to be employed for being progressively converted in a filling machine into filled and sealed packaging containers. The above-described procedure usually also includes a printing process, and also possibly further treatment to provide the packaging laminate with, for example, opening arrangements, but this is not pertinent to the invention under consideration here and is, moreover, a technique known in the art, for which reason it will not be considered in greater detail in this context.
In the subsequent production of packaging containers from a tributary or part web of packaging laminate produced in the above-outlined manner, the crease lines which were produced are utilised for progressively reforming the packaging material web into the desired container configuration. In such instance, the prior art techniques display certain drawbacks, which impedes the production of the packaging containers and leads to a poorer result. A first drawback is that the crease lines, when the packaging material is to be reformed into individual packaging containers, prove to have insufficient weakening effect on the material, which impedes the folding operation and gives less clearly defined edges on the packaging container. One reason for the poorer crease quality has proved to be the fact that the creasing is already undertaken in connection with the production of the packaging laminate, when the fibrous layer serving as carrier layer displays a relatively high moisture content deriving from the manufacturing process. In such instance, the moisture content results in the material--in connection with the creasing operation--being compressed together in an elastic rather than a plastic manner, with the result that the fibrous material compressed in the crease lines will, after storage of the wound-up part webs for some time, partly return to their original form so that the crease lines have a lower weakening effect.
A further drawback which is inherent in the described, prior art method is that the division of the relatively wide, web-shaped starting material into four to eight narrower tributary or part webs takes place in that the starting material is caused to pass a number of cutting blades uniformly disposed on a common shaft. The mutual spacing of the cutting blades is, in such instance, fixed and the transverse position of the cutting blades in relation to the web-shaped starting material is controlled by the one edge of the web. Possible errors or inaccuracies in the positioning, as well as the necessary cutting tolerances in the individual blades, will in this instance lead to the accumulation of inaccuracy across the width of the web being so great that, in unfortunate cases, the incisions are placed in poor register with the crease pattern existing in the material. More precisely, the distance between the two longitudinal edges of the part web and the longitudinal crease lines stamped in the web will not agree with the desired pattern, which impedes the forming operation and leads to undesirable circumferential variation in the finished packaging containers.
One wish in the art of packaging material manufacture is therefore to realise a method of producing crease-lined packaging material, the method obviating the above-considered drawbacks and ensuring, on the one hand, a sufficiently accurate end result in the manufacture of laminated crease-lined packaging material and, on the other hand, that the crease lines stamped in the material have the desired material-weakening properties.